Ophthalmic illuminators allow a surgeon to illuminate the interior structure of the eye such as the vitreous and the retina during surgical procedures. An endoscopic ophthalmic illuminator (endo-illuminator) includes an optical fiber within the bore of a cannula. By driving a proximal end of the optical fiber with a suitable light source, light emitted from a distal end of the fiber illuminates the desired portion of the eye. Modern small-incision techniques require a relatively high-gauge cannula such as 20 gauge (0.0295 inch diameter) or even higher gauges such as 25 gauge. But the surgeons also want sufficient luminous power from the endo-illuminator to properly illuminate the surgical field within the eye.
These two goals—using a high-gauge cannula vs. achieving sufficient luminous power are at odds with one another as follows. Because the cannula holds the optical fiber in its bore, as the gauge of the cannula is increased, the thickness of the enclosed optical fiber will need to be decreased accordingly. This decrease in the optical fiber diameter reduces the fiber's etendue, which relates to the light gathering ability for the fiber as determined by a product of the fiber's diameter and the fiber's numerical aperture. In contrast, the etendue for an endo-illuminator light source such as a conventional light-emitting diode (LED) is relatively high. Under the law of conservation of etendue, light must be lost when a high-etendue source drives a low-etendue fiber. In other words, only that portion of light from the source subtended by the optical fiber's etendue will couple to the optical fiber. The remainder of the light from the source must be lost. This is not an issue when a highly luminous source such as a xenon, halogen, or high-intensity discharge (HID) bulb is used as the endo-illuminator source in that the fraction of the light output from such relatively powerful sources coupled to the fiber is of sufficient luminous power to satisfactorily illuminate the surgical field. But such conventional non-solid-state sources produce a relatively large amount of heat while consuming substantial power. In contrast, an LED source for an endo-illuminator is much cooler and consumes less power, making it more suitable for battery-powered applications. Moreover, an LED source would be safer as LEDs are less prone to burning out during surgical procedures as compared to conventional bulb sources. In addition, LEDs are less costly as compared to halogen or HID sources. Although LEDs thus make an attractive alternative to the conventional use of HID or halogen bulbs, their luminous power is typically less than a conventional bulb source. Thus, due to the relatively high etendue of a conventional LED and its relatively low luminous power, the conventional LED will not pass sufficient light energy into a low etendue optical fiber.
Accordingly, there is a need in the art for an improved ophthalmic illuminator that enjoys the advantages of an LED source yet provides sufficient luminous power to the surgical field within the eye.